91 C1500 4.3L Possible Bad Fuel Pump?

I have a 91 C1500 4.3L. Here lately It has been having issues accelerating when I make it into 3 and 4 gear. If I drive for a few days it typically goes away however if I let it set a day the problem comes back. At time it will not want to start after shutting it off. Just replaced the air filter and fuel filter and it worked fine for a day however I went 1 day without driving and the problem is back. Any ideas? Do you think the Fuel Pump is bad?

Check fuel pressure on a cold start for up to specs.
Z code eng turbo = 35-38
All other gas engines 9-13 lbs.
Has it ever had a good tune up?
Any check engine lights on?

I changed all the wires and plugs last fall.

Last fall was a year ago.
How many miles on it since than?
Always recheck check cap and rotor and plugs and wires.
Good hot blue spark to all plugs?
Ac delco plugs?
Pull plugs when it does it and check for wet on end or dirty plugs.

When it does it always check for goos spark and check fuel pressure and post back fuel pressure readings.
Does engine crank over good?
Any codes or check engine lights?